Quantitative Analysis of Repaired and Unrepaired Damage to Trilobites from the Cambrian (Stage 4, Drumian) Iberian Chains, ne Spain

Abstract

Repaired fossil skeletons provide the opportunity to study predation rates, repair mechanisms, and ecological interactions in deep time. Trilobites allow the study of repaired damage over long time periods and large geographic areas due to their longevity as a group, global distribution, and well-preserved mineralized exoskeletons. Repair frequencies on trilobites from three sites representing offshore marine environments in the Iberian Chains (Spain) show no injuries on 45 complete redlichiid thoraces from Minas Tierga (Huermeda Formation, Cambrian Series 2, Stage 4), or 23 complete Eccaparadoxides pradoanus thoraces from Mesones de Isuela (Murero Formation, Cambrian Series 3, Drumian). Ten injuries on 69 E. pradoanus thoraces from Purujosa (Murero Formation, Cambrian Series 3, Drumian) were noted. There is no evidence for laterally asymmetric predation or size selection on the trilobites in this study. Weak evidence for selection for the rear of the thorax is documented. A series of injured trilobites illustrates four stages of the healing process. Analysis of injury locations and frequency suggests that injuries to these trilobites are predatory in origin. Semilandmark analysis of previously described exoskeletons with unrepaired damage assigned to the ichnotaxon Bicrescomanducator serratus alongside newly collected damaged exoskeletons from Purujosa (Mansilla and Murero Formations, Stage 5, Drumian), Mesones de Isuela (Murero Formation, Drumian), and Minas Tierga (Huermeda Formation, Stage 4) found that shapes of biotic and abiotic breaks could not be distinguished.